1. Field of the Invention
This invention relates to a system for correcting the light measurement of a camera with an aperture correction factor upon changes in light measuring modes.
2. Description of the Prior Art
In general, the brightness of a scene to be photographed is not uniform. For example, its central portion may be brighter than the surrounding portion, or conversely the surrounding portion may be brighter than the central portion. When the difference between the brightnesses of these portions is small, one can use an average light measuring mode and still be assured that the measured light value does not deviate much from the true one. However, when the brightness of the various portions of the object differ to any great extent the overall view field light measuring mode does not always control exposures with any high degree of accuracy. For example, when the surrounding area in the finder image is far brighter than that of the central area, the light sensor is influenced significantly by the intensity of light coming from the surrounding area. Hence, the light measurement system tends not to recognize the brightness of the central area but only at the brightness of the surrounding area. In that case, the measured light value merely represents an evaluation of the brightness of the surrounding area of the finder image. Therefore, if the camera is allowed to automatically set an exposure parameter or parameters at this light value, it produces an improper exposure for the central portion. In most photographic situations, the object of principal interest lies in the center of view field of the finder. Therefore, an average light measuring mode cannot give an accurate light value and is not suited for use in general-purpose cameras. In such case, it is preferable to restrict the view angle of the light sensor.
For this reason, it has been the common practice for users to change between average and spot light measuring modes depending upon a given photographic situation. This has the advantage of improving the accuracy of evaluation in complex brightness situations. Another proposal to the same end involves a plurality of photo-sensitive elements arranged on a focal plane of a collection lens and giving variable weights to the respective outputs of these elements.
In the present state of art of light measuring, however, no one has yet developed an effective method for taking into account a change in value of the aperture correction factor when evaluating the object brightness as the measurement sensitivity pattern changes.